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Rear Brake Slave Cylinders Seizing


RogerH
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Hi Folks,

I am coming near to the end of my TR4 rebuild.

The last few days I have been driving it to get the carburation sorted but found the rear brakes seizing on.

Today I spent 3 or 4 hours investigating the rear near side. What I found was was bl**dy annoying.

About 5 years ago during the rebuild I replaced the near side cylinder as it was leaking (I should have just replaced the seals). A ywar later I had to replace the offside also. 

Today I found that the cylinder was completely seized against the back plate.  For the brakes to work correctly the cylinder needs to move freely back and forth. 

The cause ( I suspect) is that the cylinder has a groove down each side into which the captive plates sit. This groove is too narrow.

Tomorrow I shall open the groove by apprx 0.020" - hopefully the cylinder will then float into a mid position and release the brakes.

Why can't repro parts work first time.

 

Roger

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  • 2 weeks later...

I had a similar problem on my Spitfire.

I thought the retaining plates were supposed to move with the cylinder & all parts slide on the backplate. 

But if I have understood correctly, you are suggesting the retaining plates shouldn't move and the cylinder should slide relative to them.

I resolved my problem by cleaning all the crud off the backplate & both retaining plates with a wire brush so they no longer "clamped" the cylinder to the backplate, but I would be grateful to know if my understanding of how it should work is wrong.

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32 minutes ago, cliff.b said:

I had a similar problem on my Spitfire.

I thought the retaining plates were supposed to move with the cylinder & all parts slide on the backplate. 

But if I have understood correctly, you are suggesting the retaining plates shouldn't move and the cylinder should slide relative to them.

I resolved my problem by cleaning all the crud off the backplate & both retaining plates with a wire brush so they no longer "clamped" the cylinder to the backplate, but I would be grateful to know if my understanding of how it should work is wrong.

I think from reading Roger's post that the slot is too narrow so that with the retaining horseshoes fitted, it's held too tight to the backplate to move? The plates grip the cylinder and they too slide as the cylinder moves. As long as it's the cylinder that's at fault and not too-thick retainers? Can you compare?

We've had some woeful modern versions recently, might be worth letting your supplier know.

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32 minutes ago, Colin Lindsay said:

I think from reading Roger's post that the slot is too narrow so that with the retaining horseshoes fitted, it's held too tight to the backplate to move? The plates grip the cylinder and they too slide as the cylinder moves. As long as it's the cylinder that's at fault and not too-thick retainers? Can you compare?

We've had some woeful modern versions recently, might be worth letting your supplier know.

Right, at least that confirms my understanding of how its supposed to work is correct. 

My car had original type cylinders but the rear of the backplate had been painted. Removing this helped but still sticky. Cleaning the retaining plates made them a lot easier to insert and then the cylinder moved freely. 

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and as many get the horseshoes  wrong  the springy shaped fits against the back plate the flat one  fits over it and locks it all in place 

this might seem back to front but thats the way they go 

the dimples and holes in many repro ones are just  awful  the black oiled heat treated finish is the ones to use 

anything shiny is at your risk   what comes off it probably better than whats in the box of newy 

Pete

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